Single crystal wire and manufacturing method of the same

ABSTRACT

Disclosed are a single crystal wire and a manufacturing method thereof. The method comprises the steps of: placing into a growth crucible at least one metal selected from the group consisting of gold, copper, silver, aluminum and nickel; heating and melting the metal placed in the growth crucible; growing a single crystal using the metal crystal as a seed by the Czochralski or Bridgmari method; cutting the grown single crystal by electric discharge machining; and forming the cut single crystal into a wire. In the method, the grown metal single crystal is formed into a disc-shaped piece by electric discharge machining. The piece is formed into a single crystal wire by wire-cut electric discharge machining, and the single crystal wire can be used as a ring, a pendant or a wire within a high-quality cable making a connection in audio and video systems. Also, the single crystal formed into the disc-shaped piece by electric discharge machining can be used as a substrate and a target for deposition.

REFERENCE TO RELATED APPLICATIONS

This is a continuation of pending International Patent ApplicationPCT/KR2005/003050 filed on Sep. 15, 2005, which designates the UnitedStates and claims priority of Korean Patent Application No.10-2004-0075550 filed on Sep. 21, 2004.

FIELD OF THE INVENTION

The present invention relates to a single-crystal wire and amanufacturing method thereof, and more particularly to a single-crystalwire manufactured by growing a single crystal through a single crystalgrowth method and machining the grown single crystal into a wire, aswell as a manufacturing method thereof.

BACKGROUND OF THE INVENTION

The concept of high-quality cables was not generally established untilthe 1970s, but since the development of oxygen-free copper (hereinafter,referred to as “OFC”), the development of cables has rapidly progressed.

Particularly in the case of wire cables making connections in audiosystems, etc., it is well known that the quality of cables influencesthe quality of sound. Thus, replacement of low-quality cables withhigh-quality cables can provide a great improvement in sound quality.

When such wires are applied with alternating current, an alternatingmagnetic field will occur, which acts as resistance to the alternatingcurrent. Particularly, the higher the frequency, the higher theresistance, and this property is called “inductance”. In the case ofcables, if coated wires are coiled in a circular form or formed withpositive and negative terminals, the inductance will increase, resultingin a reduction in the purity of sound. However, if coated wires areformed with positive and negative terminals and then twisted like arope, the inductance will decrease instead, resulting an increase in thepurity of sound.

In general, when cables are twisted, the inductance will decrease butthe capacitance will increase to make the frequency narrower and thesound muddy. Although it is a clear fact that the sound quality of audiosystems differs depending on the cables used, the reason therefor hasnot yet been clearly established.

For example, an increase in the purity of wires leads to an increase inthe purity of sound but generally results in an increase in directcurrent resistance, which may also reduce the cable's energy. Althoughthe sound quality of cables is influenced by the material and physicalproperties of the wires themselves, it is also highly influenced by thecovering material and crystalline structure of wires, the inductance,capacitance and skin effect caused by terminal processing, and theimpedance between audio systems.

Namely, although the sound quality of most cables is influenced by theproperties of the wires themselves, it is also influenced by a coveringmaterial for the cables, the crystalline structure of the wires, etc.

Thus, OFC cables having a purity of 99.99% frequently have better soundquality than 6N copper wire cables having a purity of 99.9999%. Metalconductors for the wires include silver, gold, copper and aluminum, indescending order from highest electrical conductivity to lowest. Amongthem, copper is most frequently used as a conductor, because it isinexpensive and has good electrical conductivity and processability.

Conventional copper wires have a standard purity of 3N (99.9%), andduring production, oxygen is blown to increase the workability thereof,while copper produced in an atmosphere having no oxygen is called “OFC”.Other examples of copper wires include 6N (99.9999%), 7N (99.99999%),etc., according to the extent of removal of metals and sulfur, which areimpurities other than oxygen. Prior methods for manufacturing copperwires will now be described.

The production of tough pitch copper (hereinafter, referred to as “TPC”)is a general copper production method comprising introducing oxygen tomelt copper and rapidly cooling the melted copper. This method issuitable for mass production and produces a 3N-purity copper containingsulfur and cuprous oxide and having an oxygen content of 3000-4000 ppmand a purity of 99.9%.

OFC is copper from which the development of high-purity copper started.The OFC is a 4N (99.99%) product which has an oxygen content reduced toless than 10 ppm by removing a cuprous oxide impurity, unlike theexisting TPC process comprising blowing oxygen to cool the moltencopper. The use of the OFC allowed muddy sound to be removed and thepurity of sound to be increased, thus improving sound clarity.

Linear crystal oxygen-free copper (hereinafter, referred to as “LC-OPC”)was developed based on the theory that every factor reducing the soundquality exists at boundaries between metal crystals. When copper israpidly cooled in a melted state, it will have a fine crystal structure,in which case an increase in crystals will increasingly interfere withsignal transmission. Based on this theory, in order for the OFC to havea unidirectional crystal structure, copper is slowly cooled to obtainlarge crystals, and the resulting copper crystal structure is thenlinearly stretched. However, during the process for linearly stretchingthe copper crystal structure, mechanical stress and heat are generatedin the copper, so that the copper crystal structure is adverselyaffected, thus causing deterioration in sound quality.

Pure crystal ohno continuous casting (hereinafter, referred to as“PCOCC”) was developed to complement the shortcoming of the LC-OPC, inwhich, during the process for linearly stretching the copper crystalstructure, mechanical stress and heat are generated in the copper, sothat the copper crystal structure is adversely affected, thus causingdeterioration in sound quality. This continuous casting is produced as asingle crystal by using an additional structure for slow cooling.

Typical examples of conductors having a high strength include LC-OFC andPCOCC, which have not been subjected to a thermal treatment process inorder to prevent their single crystal structure from being changed.However, the copper wires, which have not been subjected to the thermaltreatment process, undergo mechanical stress during their machining sothat their crystal structure is influenced. To solve this shortcoming, amyu (m) conductor was developed which has been slightly thermallytreated to reduce mechanical stress. In the existing technologies fordeveloping wires, it can be seen that the structure of a single crystalacts as an important factor in manufacturing high-quality cables.However, technology for preventing the single crystal structure frombeing changed has not yet been developed.

Meanwhile, silver (Ag) has excellent electrical properties, particularlylow electrical resistance, compared to copper. Thus, in audio cables,silver is clearly advantageous compared to copper, particularly when inan oxidized state. Namely, copper is easily oxidized to form a coatingfilm such as a semiconductor film, whereas oxidized silver has anadvantage in that it is chemically stable, so that it can sufficientlyfunction as a conductor.

Like the case of copper wires, silver conductors have been continuouslyimproved through an increase in their purity and by the use of thermaltreatment. Thus, it is known that recent silver wire and silver-coatedOFC wire developed for exclusive use in audio systems carry a lot ofinformation and produce smooth sound, unlike a silver wire for use ingeneral telecommunication.

Aluminum is a conductor having highly specific properties, like silver.It is known that aluminum is slightly higher in electrical resistancethan copper but also that it produces a highly specific sound in a widesound range. Thus, an aluminum wire containing silver or aluminumproduces a unique and elegant sound.

Accordingly, to ensure high-quality cables, technology for manufacturinga copper, silver or aluminum wire using a high-purity single crystalurgently needs to be developed.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made to solve theabove-described problems occurring in the prior art, and it is an objectof the present invention to provide a method for manufacturing a singlecrystal wire, comprising growing a metal single crystal using a seedcrystal and then forming the grown metal single crystal into adisc-shaped piece which is then formed into a wire.

To achieve the above object, the present invention provides a method formanufacturing a single crystal wire, comprising the steps of: placinginto a growth crucible at least one metal selected from the groupconsisting of gold, copper, silver, aluminum and nickel; heating andmelting the metal placed in the growth crucible; growing a singlecrystal using the metal crystal as a seed by the Czochralski or Bridgmanmethod; cutting the grown single crystal by electric dischargemachining; and forming the cut single crystal into a wire.

In the inventive method, the growth crucible is preferably selected fromthe group consisting of a graphite crucible, a boron nitride (BN)crucible, an alumina crucible, and a quartz crucible. The heating of themetal placed in the growth crucible is preferably performed using an RFinduction coil or a carbon heater. Also, in the cutting step, the singlecrystal is preferably formed into a disc shape. After the cutting step,the cut single crystal is preferably formed into a wire by wire-cutelectric discharge machining or press machining using a mold having apattern. Also, the single crystal formed into the disc shape ispreferably used as a metal single crystal substrate or a metaldeposition target. Also, the wire formed by the pressing machining has aring shape.

Moreover, in the cutting step, the single crystal is preferably formedinto a cylindrical shape. Also, the cylindrical shape formed in thecutting step is preferably cut into a ring shape. Also, after thecutting step, the single crystal is preferably subjected to a polishingor wet etching process.

Also, the wire is preferably covered with synthetic resin on the outersurface thereof, and both ends of the wire are provided with terminals.

In another aspect, the present invention provides a single crystal wiremanufactured by: heating and melting at least one metal selected fromthe group consisting of gold, copper, silver, aluminum and nickel;growing a single crystal using the metal crystal as a seed by theCzochralski or Bridgman method; and cutting the grown single crystal.

Herein, the cut single crystal is preferably formed into a ring shape ora wire shape for use as a connection cable.

Also, the connection cable formed into the wire shape is preferablycovered with synthetic resin on the outer surface thereof, and both endsof the connection cable are preferably provided with terminals.

According to the present invention, the metal single crystal is grownusing the seed crystal and then formed into a disc-shaped piece byelectrical discharge machining, and the piece is subjected to wire-cutdischarge machining. Accordingly, various single-crystal wires and wireproducts having a unidirectional crystal structure can be formed.

Also, the single-crystal wire can be used as products, such as a ring, apendant or a wire in a high-quality cable making a connection in audioand video systems.

In addition, the single crystal formed into the disc shape can be usedas a single crystal substrate for the fabrication of thin films or atarget for metal deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph showing a copper-single crystal formed accordingto an embodiment of the present invention.

FIG. 2 is a photograph showing a wire formed according to an embodimentof the present invention.

FIG. 3 is shows a disc-shaped single crystal piece and mold according toan embodiment of the present invention.

FIG. 4 shows the step of machining a single crystal into a ring shape,according to an embodiment of the present invention.

FIG. 5 shows XRD results for a copper single-crystal wire and apolycrystal copper wire.

FIG. 6 shows GDS results for a copper single-crystal wire and apolycrystal copper wire.

FIG. 7 shows surface image photographs of a copper single crystal wire(a) and a polycrystal copper wire (b).

FIG. 8 shows the comparison of resistivity between a copper singlecrystal wire and a polycrystal copper wire.

FIG. 9 shows sound cables produced by covering the outer surface ofcopper single crystal wires with insulation leather.

FIG. 10 shows the comparison of impedance as a function of frequencybetween a single crystal cable and a polycrystal cable.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings.

First, a metal mass to be grown, which is at least one selected from thegroup consisting of gold, copper, silver, aluminum and nickel, is placedinto a growth crucible (BN crucible, quartz crucible, graphite crucible,alumina crucible, etc.) in which the metal mass is then melted either byinduction heating using an induction coil or by a carbon heater. Thegrowth crucible used in the present invention is either the graphitecrucible or a double crucible structure in which the outer crucible isthe graphite crucible and the inner crucible is one selected from amongthe BN crucible, the quartz crucible and alumina crucible.

The growth of a copper or silver single crystal will now be described indetail.

Since copper and silver are not chemically bound to carbon, the graphitecrucible or the double crucible structure having the graphite crucibleas an outer crucible is used as the growth crucible. The reason why thegrowth crucible is used as a heating element is that the temperature ofinduction heating will be difficult to control when the amount of meltedmass remaining in the crucible during the growth of a metal singlecrystal is reduced. Thus, it is easy in the growth of a metal singlecrystal to use the growth crucible as a heating element to control thetemperature of the crucible itself. The growth crucible, copper andsilver are induction-heated to the melting points of the metals. Sincethe melting points of copper and silver are 1083° C. and 962° C.,respectively, they are heated to temperatures higher than the meltingpoints by about 30° C. so as to dissolve them completely.

A seed crystal having the desired crystal structure is prepared andgrown into a single crystal by the Czochralski method. The seed crystalis prepared in the form of a rod in each of the (100), (110) and (111)directions. The growth of the copper single crystal is performed at atemperature of 1100-1000° C., and the growth of the silver crystal isperformed at a temperature of 1000-900° C. Also, the growth of each ofcopper and silver is performed according to the Czochralski method, inwhich the temperature of a liquid phase is lowered at a rate of about 1°C./min.

Although the method for growing the single crystal using the Czochralskihas been described above, the Bridgman method may also be used for thegrowth of single crystals, and the use of the Bridgman method is alsowithin the scope of the present invention.

According to the above procedure, a copper single-crystal as shown inFIG. 1 is formed.

Then, the formed single crystal is used to produce a wire. For thispurpose, the grown high-purity single crystal is cut into a disc-shapedpiece having the desired thickness by electric discharge machining. Inthis regard, the electric discharge machining is adopted in order tominimize deformation caused by stress generated in machining copper andsilver into the disc-shaped piece.

The thickness of the disc-shaped piece is determined depending on thediameter of a wire to be produced, and in the present invention, thedisc-shaped disc has a small thickness of about 1 mm.

Since the produced disc-shaped piece should be formed into a1-mm-diameter wire by wire-cut electric discharge machining, it ispolished with alumina powder having a particle size of 0.3 μm in orderto completely remove stress remaining on the surface of the disc-shapedpiece.

To obtain the desired wire from the disc-shaped piece subjected to thepolishing step, the disc-shaped disc is fixed using an outer mold andthen formed into a wire by wire-cut electric discharge machining. Toform the wire from the disc-shaped piece, the disc-shaped piece is cutfrom the outside to the inside of a cross-section thereof so as to forma wire having the desired thickness, and a separate winding process isperformed to prevent twisting of the wire during the electric dischargemachining.

Alternatively, the wire may also be formed by forming a small hole inthe central portion of the disc using a wire drill and then cutting thedisc from the inside to the outside of a cross section thereof so as toform a wire having the desired diameter.

Since the wire obtained according to the above process has the effect ofstress due to the machining step, optical polishing of the wire isrequired. This optical polishing is performed using alumina powder inthe same manner as in the polishing of the disc-shaped piece so as toremove the effect of stress remaining on the surface of the wire.

Alternatively, the effect of stress formed on the surface of the wiremay also be removed using a hydrofluoric acid dilution. The effects ofstress on the metal surface during the electric discharge machiningmostly consist of oxide films. Such oxide films can be removed through awet etching process using a solution of H₂O:HF=5:1, in which the wetetching is performed for about 3 minutes.

The wire produced through this process is shown in FIG. 2.

The surface-polished or wet-etched wire can be used as a connectioncable making connections in audio systems, etc. For use as the cable,the wire is covered with any material on the outer surface thereof.

The process for covering the wire is performed by a known method or amanual process to make a cable. Thus, the single crystal wire productrequired for the transmission of commercial sounds and image data isproduced.

Generally, the wire is covered with, for example, an insulatingshrinkable tube having a diameter larger than that of the wire. Namely,for use as a sound cable, the wire is covered with a polyurethane orinsulating shrinkable tube to the required diameter so as to produce asingle crystal wire product in which the wire is protected fromoxidation or external stress.

Also, for use as a coaxial cable, the wire is covered sequentially witha synthetic resin coating and a natural leather coating so as to producea single-crystal product which is protected from the noise of externalcurrent. Also, both ends of the cable are terminated with RCA terminalsor terminals made of metal single crystals so that the cable isprotected from noise during use as a connection in audio and videosystems, thus increasing the quality of sound.

Although the method for forming the wire using the disc-shaped piece hasbeen described herein, the disc-shaped piece may also be used as aunidirectional substrate or target for deposition, in which case it canbe used a target having a size of 2, 3 or 4 inches. In order for thedisc-shaped piece to have a precise outer diameter, the disc-shapedpiece formed by electric discharge machining is re-machined to thedesired diameter, or the copper single crystal is subjected to electricdischarge machining to have the desired outer diameter, so that it canbe used as a target or substrate for deposition. This process is alsowithin the scope of the present invention.

Although the method for forming the wire by electric discharge machininghas been described above, the wire may also be formed using a mold asshown in FIG. 3.

As shown in FIG. 3, a disc-shaped piece 100 formed by electric dischargemachining is placed on a mold 100 having the desired pattern 111 formedthereon and then subjected to press machining, so as to form a wirehaving the same shape as the pattern 111 of the mold 110. Namely, whenthe mold 110 having the pattern 111 as shown in FIG. 3 is used, aring-shaped wire will be obtained, and when a mold having patternscontinuously connected with each other is used, a continuous wire willbe obtained.

In this regard, the ring-shaped wire can be used as a ring or pendant,and the continuous wire is subjected to post-machining, such as opticalpolishing, in the same manner as when forming the wire by millingoperations, including electric discharge machining, so as to produce asingle-crystal cable. Alternatively, the continuous wire is subjected towet etching to remove an oxide film from the surface thereof so as toproduce a single-crystal cable.

Although the continuous single crystal wire cable has been describedabove, the single crystal grown according to the Czochralski or Bridgmanmethod as described above can be used to produce a highly pure ring. Forthis purpose, the upper surface of the single crystal grown as shown inFIG. 1 is cut with a wire-cut electric discharge machine. Then, as shownin FIG. 4, the resulting crystal is cut into a column shape using a wireelectric discharge drill having a diameter of less than 0.5 mm and awire-cut electric discharge machine. Then, the column-shaped material issubjected to electric discharge machining to form a cylindrical body120, which is then cut in the horizontal direction to produce a highlypure ring. The machining of the metal using the electric dischargemachine is performed using known technology. However, to prevent theoxidation of the product and to give high-added value to the product byfine machining, it is also possible to use spearhead machines, such asnon-electric discharge machines.

The ring products manufactured according to the above method may be usedas an aid for promoting human health. In the ring containing metal atomsarranged in one direction, a change in the magnetic field induced by anelectric current in the ring or an eddy current induced by this changein the magnetic field will be increased compared to that in a generalmetal ring. Namely, in the ring having metal atoms arranged in onedirection, factors interfering with electric current will be reducedowing to its structural stability so that the amount of electric currentinduced in the ring will be larger than that in a general metal ring.Thus, the amount of eddy current produced in the single crystal ringwill stimulate the blood flow of the human body to make it smooth, andwhen biomagnetic changes caused by this change in the blood flow areaccumulated over time, the change of the blood flow becomes activecompared to that in a general person. The fact that smooth and activeblood flow is favorable to the health of the human body is wellsupported by modern medical science.

In order to examine whether the high-purity single crystal wire preparedby the above method overcomes the problems of the existing crystalstructure, the single crystal wire produced using the copper-singlecrystal, and a polycrystal copper wire cured in a molten state, wereanalyzed using XRD. The analysis results are shown in FIG. 5.

As can be seen in FIG. 5, the single-crystal wire produced by the abovemethod had a unidirectional crystal structure similar to that of theseed crystal.

Also, to examine the contents of impurities required for use as acommercial wire, the polycrystal copper and the single crystal wereanalyzed by glow discharge spectroscopy, and the results are shown inFIG. 6.

As can be seen in FIG. 6, the produced single crystal had a purity of5N, indicating that it can be used as a wire.

The surface of the produced single-crystal wire and the surface of apolycrystal copper wire were etched and the results are shown in FIG. 7.

As can be seen in FIG. 7, in the polycrystal wire, an etching patternshowing the crystal direction was not formed, but in the single-crystalwire, a square etched pattern showing the (100) direction was formed.

The above results suggest that the produced single crystal wire is asingle crystal, which is highly pure and has a unidirectional crystalstructure.

This single crystal wire was measured for resistivity with a change intemperature, and the results are shown in FIG. 8.

The resistivity of the polycrystal copper wire is known to be 1.7×10⁻⁶Ωcm for highly pure copper. As can be seen in FIG. 8, however, theresistivity of the single crystal wire prepared according to theinvention was 1.2×10⁻⁷ Ωcm and was much lower with a decrease intemperature than that of the polycrystal copper wire.

As shown in FIG. 9, the single crystal wire was finally covered withnatural leather on the outer surface thereof. As a result, the inventivecable was markedly superior in sound signal transmission to the existingpolycrystal product. This is demonstrated from results shown in FIG. 10.

As can be seen in FIG. 10, in the single crystal wire, the inventivesingle crystal cable was completely protected from external sound andmagnetic waves owing to the characteristics of the natural leather.Thus, the impedance as a function of frequency was constantly lower overthe entire frequency region than that of the existing polycrystal cable.

The single crystal wire manufactured by the present invention and themanufacturing method thereof is applicable in various fields.Particularly, the present invention can be applicable for commercialimage and sound cables, precious metal rings and various medicalaccessories, and thus, is an excellent technology from an industrialpoint of view.

1. A method for manufacturing a single crystal wire, comprising thesteps of: placing into a growth crucible at least one metal selectedfrom the group consisting of gold, copper, silver, aluminum and nickel;heating and melting the metal placed in the growth crucible; growing asingle crystal using the metal crystal as a seed by the Czochralski orBridgman method; cutting the grown single crystal by electric dischargemachining; and forming the cut single crystal into a wire.
 2. The methodof claim 1, wherein the growth crucible is one selected from the groupconsisting of a graphite crucible, a boron nitride (BN) crucible, analumina crucible, and a quartz crucible.
 3. The method of claim 1,wherein the heating of the metal placed in the growth crucible isperformed using an RF induction coil or a carbon heater.
 4. The methodof claim 1, wherein, in the cutting step, the single crystal is formedinto a disc shape.
 5. The method of claim 4, wherein, after the cuttingstep, the cut single crystal is formed into a wire by wire-cut electricdischarge machining or press machining using a mold having a pattern. 6.The method of claim 4, wherein the disc-shaped single crystal is used asa metal single-crystal substrate or a target for metal deposition. 7.The method of claim 5, wherein the wire formed by the pressing machiningis in the form of a ring.
 8. The method of claim 1, wherein, in thecutting step, the single crystal is formed into a cylindrical shape. 9.The method of claim 8, wherein the cylindrical single crystal formed inthe cutting step is cut into a ring shape.
 10. The method of claim 1,which further comprises, after the cutting step, the step of polishingor wet-etching the single crystal.
 11. The method of claim 5, whereinthe wire is covered with synthetic resin on the outer surface thereof.12. The method of claim 11, wherein the synthetic resin is covered withnatural leather on the outer surface thereof.
 13. The method of claim11, wherein both ends of the wire are provided with terminals.
 14. Asingle crystal wire manufactured by: heating and melting at least onemetal selected from the group consisting of gold, copper, silver,aluminum and nickel; growing a single crystal using the metal crystal asa seed by the Czochralski or Bridgman method; and cutting the grownsingle crystal.
 15. The single crystal wire of claim 14, wherein the cutsingle crystal is formed into a ring shape.
 16. The single crystal wireof claim 14, wherein the cut single crystal is formed into a wire shapefor use as a connection cable.
 17. The single crystal wire of claim 16,wherein the connection cable formed into the wire shape is covered withsynthetic resin on the outer surface thereof.
 18. The single crystalwire of claim 17, wherein the synthetic resin is covered with naturalleather on the outer surface thereof.
 19. The single crystal wire ofclaim 17, wherein both ends of the connection cable are provided withterminals.